1. Field of the Invention
The present invention relates to plasma processing apparatuses and, more particularly, to a plasma processing apparatus having a dielectric plate through which a microwave is introduced into a process chamber so as to generate plasma in the process chamber.
2. Description of the Related Art
In recent years, a plasma processing apparatus is used to perform a film deposition process, an etching process or an ashing process in a manufacturing process of semiconductor devices since the semiconductor devices have become more densified and a finer structure. For example, in a typical microwave plasma processing apparatus, a 2.45 GHz microwave is introduced into a process chamber through a slot electrode. An object to be processed such as a semiconductor wafer or an LCD substrate is placed inside the process chamber, which is maintained under a negative pressure environment by a vacuum pump. Additionally, a reactant gas is also introduced into the process chamber so that the process gas is converted into plasma by the microwave. Thus, active radicals and ions are generated, and the radicals and ions react with the object to be processed, which achieves a film deposition process or an etching process.
Generally, the microwave is introduced into the process chamber from a slot electrode by being passed through a dielectric plate. The dielectric plate serves as a top plate of the process chamber so as to hermetically seal the process chamber. The dielectric plate must be made of a dielectric or insulating material so as to let the microwave passes therethrough.
Since the microwave has a nature of wave propagation, a standing wave is generated as a resultant wave of a synthesis of a progressing wave traveling along the front surface of the dielectric plate and a regressive wave reflected by the back surface of the dielectric plate. Conventionally, the thickness of the dielectric plate is determined so that a transmission rate of the microwave with respect of the dielectric plate is maximized.
However, the inventor of the present invention found that the dielectric material of the dielectric plate isolates by a plasma ion energy applied by transmission of a microwave isolates the material of the dielectric plate. If the material of the dielectric plate isolates, the material enters the object to be processed as impurities. On the other hand, if the transmission rate of the microwave with respect to the dielectric plate is reduced so as to prevent the isolation of the material of the dielectric plate, a plasma processing speed is reduced which results in deterioration of a yield rate.
It is a general object of the present invention to provide an improved and useful plasma processing apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a plasma processing apparatus which can apply a high-quality process to an object to be processed by preventing impurities from being generated due to a microwave transmitting through a dielectric plate.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a dielectric plate adapted to be provided between a process chamber of a plasma processing apparatus and a slot electrode guiding a microwave used for a plasma process, wherein a thickness H of the dielectric plate has a predetermined relationship with a wavelength xcex of the microwave in the dielectric plate so that an amount of isolation of the dielectric plate due to transmission of the microwave is minimized, the wavelength xcex being represented by xcex=xcex0n, where xcex0 is a wavelength of the microwave in a vacuum and n is a wavelength reducing rate of the dielectric plate represented by n=1/(xcex5t)xc2xd, where xcex5t is a specific dielectric rate of the dielectric plate in a vacuum.
According to the present invention, the thickness H of the dielectric plate is determined based on the relationship with the wavelength xcex of the microwave in the dielectric plate. When the thickness H of the dielectric plate is 0.5 times the wavelength xcex of the microwave in the dielectric plate, a standing wave is generated as a resultant wave of a synthesis of a progressing wave traveling along the front surface of the dielectric plate and a regressive wave reflected by the back surface of the dielectric plate. Thereby, the reflection is maximized and a power of the microwave transmitted to the process chamber 102 is minimized. In such a case, generation of plasma is insufficient, and, thereby a desired process speed cannot be achieved.
On the other hand, when thickness of the dielectric plate is 0.75 times the wavelength xcex of the microwave in the dielectric plate, the transmission power of the microwave is maximized but ion energy in the plasma is also maximized. A plasma ion energy applied by transmission of a microwave isolates the material of the dielectric plate. If the material of the dielectric plate isolates, the material enters the object to be processed as impurities, thereby deteriorating a high-quality plasma process.
In order to supply a microwave having a sufficient power but prevent the dielectric plate from being isolated, the predetermined relationship between the thickness H and the wavelength xcex of the dielectric plate is preferably represented by 0.5xcex less than H less than 0.75xcex. More preferably, the thickness H of the dielectric plate satisfies a relationship represented by 0.6xcexxe2x89xa6Hxe2x89xa60.7xcex.
Alternatively, the predetermined relationship between the thickness H and the wavelength xcex of the dielectric plate may be represented by 0.3xcex less than H less than 0.4xcex.
In general, the predetermined relationship between the thickness H and the wavelength xcex of the dielectric plate is represented by one of the relationships (0.1+0.5 N)xcexxe2x89xa6Hxe2x89xa6(0.2+0.5 N)xcex and (0.3+0.5 N)xcexxe2x89xa6Hxe2x89xa6(0.4+0.5 N)xcex, where N is an integer.
Additionally, there is provided according to another aspect of the present invention a plasma processing apparatus comprising: a process chamber in which a plasma process is applied to an object to be processed; a slot electrode having a plurality of slits guiding a microwave introduced into the process chamber so as to generate plasma in the process chamber; and a dielectric plate provided between the slot electrode and the process chamber, wherein a thickness H of the dielectric plate has a predetermined relationship with a avelength xcex of the microwave in the dielectric plate so that an amount of isolation of the dielectric plate due to transmission of the microwave is minimized, the wavelength xcex being represented by xcex=xcex0n, where xcex0 is a wavelength of the microwave in a vacuum and n is a wavelength reducing rate of the dielectric plate represented by n=1/(xcex5t)xc2xd, where xcex5t is a specific dielectric rate of the dielectric plate in a vacuum.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction of the accompanying drawings.